Dilute Diet Research Articles

Water management in nectar-feeding birds

nectarivory is widespread in birds, but best known in three unrelated families on different continents: the American hummingbirds, Australasian honeyeaters, and the sunbirds of Africa and Asia. Bird pollinators require substantial nectar rewards and their flowers produce copious nectar, which is,

Dietary intake effects on arginine vasotocin and aldosterone in cloacal fluid of whitebellied sunbirds ( Nectarinia talatala)

The main objective of this study was to determine whether or not the renal outputs of the osmoregulatory hormones arginine vasotocin (AVT) and aldosterone (ALDO) reflect the osmotic status of whitebellied sunbirds ( Nectarinia talatala). The birds were fed a range of sucrose concentrations (from 0.07 to 2.5 mol/l, with osmolalities of 70 to ∼5,800 mosM/kg), and adjusted their intakes so that they drank large volumes of dilute diets and small volumes of concentrated diets. Renal fluid outputs were appropriately regulated so that large volumes of cloacal fluid (CF) were voided on the dilute diets and small volumes on the concentrated diets. Accordingly, plasma AVT concentrations increased with increasing sugar concentration; however, AVT outputs in CF did not change in a similar manner, rather they decreased as dietary concentration increased. It was not possible to measure plasma ALDO concentrations in the small sunbirds because of insufficient blood samples available; however, ALDO outputs in CF did vary with the sucrose diets and renal function, being highest on the most concentrated diet. In addition ALDO output in CF fell markedly when sodium was added to the 0.5 mol/l sucrose diet. We conclude that in sunbirds fed increasingly concentrated sucrose solutions, changes in CF outputs of ALDO, but not AVT, appear to reflect the water flux and hydration state of these birds.

Osmoregulatory response to acute diet change in an avian nectarivore: rapid rehydration following water shortage

Nectarivores may be required to switch between water conservation and water excretion as rapidly as they change food plants in nature. We examined the rehydration response in Whitebellied Sunbirds ( Nectarinia talatala) that had been fed a concentrated sucrose diet (2.5 mol/l) for 2 days and then were switched to a diet 10× less concentrated (0.25 mol/l) on the morning of the third day. We measured water gain as well as cloacal fluid (CF) volume hourly over 12 h, and analysed CF osmolality and calculated osmotic excretion. CF was also assayed for the osmoregulatory hormone aldosterone (ALDO). As in most water-deprived birds, whitebellied sunbirds cope with water shortage when fed a concentrated sugar diet by almost completely ceasing to void CF. Although osmolality of CF is high, volumes are not sufficient to maintain a steady rate of excretion and the birds retain osmolytes. Immediately upon switching to dilute diet, sunbirds produce copious volumes of CF and osmotic excretion is elevated and maintained at high levels over the first 6 h of rehydration. This stabilises by the afternoon at levels expected for hydrated birds. Some 2–3 h after peak osmotic excretion, there is a peak in the discrepancy between water intake and output, mirrored in an increase in ALDO output. These data suggest that excretion of retained osmolytes is undertaken as soon as water is available, with changes in the body fluid composition occurring subsequently. This study vindicates the use of CF to obtain repeated measurements of changes in the osmoregulatory steroid ALDO in small birds.

Concentration and temperature effects on sugar intake and preferences in a sunbird and a hummingbird

1. The nectars of hummingbird- and passerine-pollinated plants differ in both sugar type and concentration. Firstly, hummingbird nectars tend to be more concentrated than passerine nectars. Secondly, sucrose dominates hummingbird nectars, whereas glucose and fructose (hexose sugars) are the prevalent sugars in nectar of almost half the passerine-pollinated plants. It has been commonly assumed that these differences can be attributed to selection pressure from birds, largely determined by avian sugar preferences and digestive physiology. 2. Intake and preferences of Whitebellied Sunbirds Nectarinia talatala (A. Smith) and Broadtailed Hummingbirds Selasphorusplatycercus (Swainson) were examined across a range of sucrose and equicaloric hexose solutions at two ambient temperatures. Hummingbird energy balance was not affected by sugar type. Sunbird energy balance was only influenced by sugar type on a very dilute diet (0.1 mol l-1 sucrose equivalents, 'SE'), when the birds ingested 12% more sucrose than hexoses. Sunbirds and hummingbirds showed similar patterns in sugar preferences. Sunbirds preferred hexoses when offered dilute diets (0.1 mol l-1 SE at 21°C) and showed slight preference for sucrose when offered more concentrated diets (significant at 0.75 mol l-1 SE). Hummingbirds showed slight (non-significant) hexose preference when offered a dilute diet (0.25 mol l-1 SE at 10°C), but, in contrast to previous findings, hummingbirds showed no significant sucrose preference. 3. Our findings for Whitebellied Sunbirds and Broadtailed Hummingbirds do not support an ornithocentric explanation for nectar composition. Plant physiology and opportunist nectar feeders may also be influencing nectar sugars. To further address this question we discuss methodological considerations for researchers investigating how avian preferences and physiology may affect nectar composition.

The effect of dry matter concentration of liquid diets on the growth performance of grower-finisher pigs

There is a considerable body of information on the voluntary feed intake of pigs fed on dry diets. However, there is a paucity of information on the factors affecting feed intake of pigs fed liquid diets. Pigs have a limit to their volumetric intake and will normally maximise dry matter intake when fed dry diets, ad libitum. For pigs fed dry feed the requirement for water per unit of dry matter will be dependent upon the composition of the feed and the requirement for renal clearance of nitrogen and minerals. What is not clear, is whether presenting the feed mixed with water results in excessive water intake that produces a point loading of the stomach, which in turn limits voluntary feed intake, i.e. whether physical bulk limitations override the normal homeostatic control. Therefore, it is not possible to extrapolate from data generated with dry fed pigs and anticipate voluntary intake of pigs fed dilute liquid diets. The aim of this study was to determine the effect of dry matter concentration of liquid feed on feed intake and growth performance of grower-finisher pigs.

The role of food distribution and nutritional quality in behavioural phase change in the desert locust

The behaviour of herbivorous insects is influenced by their nutritional state. Nutrition-induced behavioural changes are often interpreted as adaptive mechanisms for controlling nutrient intake; however, their influence on other life history traits has received far less attention. We investigated the effect of food quality and distribution on the behaviour and phase state of desert locusts, Schistocerca gregaria Forskål (Orthoptera, Acrididae), which change from the ‘solitarious’ to the ‘gregarious’ phase in response to population density. Phase change involves many morphological, physiological and behavioural changes. Solitarious insects are cryptic whereas gregarious locusts aggregate. Individual phase change is stimulated by mechanical contact with other locusts. A clumped resource distribution promotes change to the gregarious phase by increasing crowding and contact between individuals. In this study, we found that the effect of food distribution on locust phase depended on the nutritional quality of the food. We used three synthetic food treatments: near optimal, dilute and a choice of two unbalanced but complementary foods. Clumped resource distribution led to increased gregarization in the dilute and the complementary diet treatments. This effect was particularly pronounced on the complementary foods, owing to the interaction of crowding and locomotion. Gregarization was most pronounced in the dilute diet treatment, owing to increased activity. These diet-induced effects are explained in terms of behavioural changes in locomotion, quiescence and feeding that are consistent with what is known from earlier work on locust feeding behaviour and behavioural phase change.

Evaluation of Bt Transgenic Sweet Corn Hybrids for Resistance to Corn Earworm and Fall Armyworm (Lepidoptera: Noctuidae) using a Meridic Diet Bioassay2

A laboratory bioassay was used to evaluate Bt transgenic sweet corn hybrids for resistance against the corn earworm, Helicoverpa zea (Boddie), and the fall armyworm, Spodoptera frugiperda (J. E. Smith). Whorl leaves, silks, and kernels, either fresh or oven-dried and ground with a mill, were incorporated into a dilute pinto bean diet and bioassayed against neonate, 3-, or 6-day-old larvae. Regardless of age of the larvae, results with the diet bioassay using fresh silks, oven-dried silks or fresh kernels were highly correlated with those for the fresh silk bioassay. Differences in susceptibility between insect species to the CrylA(b) toxin produced in the transgenic plants were also readily discernable using the diet bioassay. Based on results of the bioassays, Novartis sweet corn hybrids containing a crylA(b) gene gene for δ-endotoxin production were very highly resistant to leaf, silk and kernel feeding by the corn earworm and highly resistant to leaf and silk feeding by the fall armyworm.

Conservation Implications of Dietary Dilution from Debris Ingestion: Sublethal Effects in Post‐Hatchling Loggerhead Sea Turtles

Abstract: Ingestion of anthropogenic debris by marine species has been documented extensively; fewer studies have attempted to quantify the sublethal effects caused by debris ingestion. One potential sublethal effect is reduced nutrient gains from diets diluted by consumption of debris. Post‐hatchling and juvenile loggerhead sea turtles (Caretta caretta) consume substantial quantities of debris. We evaluated the effects of dietary dilution on voluntary intake in post‐hatchling loggerheads to assess their ability to compensate for the presence of inert diluents in their diet by increasing dry mass intakes to maintain nutrient gains. Mean daily intakes of dry mass did not increase significantly with dietary dilution, so intakes of energy and nitrogen on a 50% dilution diet were significantly lower than on a 10% dilution diet. Therefore, post‐hatchling loggerheads have an extremely limited ability to compensate for dietary dilution and would experience sublethal effects from decreased energy and nitrogen gains on dilute diets. Decreased nutrient intakes have serious conservation implications because of possible decreased growth rates, longer developmental periods at sizes most vulnerable to predation, depleted energy reserves, reduced reproductive output, and decreased survivorship.

Renal function in red wattlebirds in response to varying fluid intake

Red wattlebirds (Anthochaera carunculata) are among the more nectarivorous of the Australian honeyeaters (family Meliphagidae). As such, they potentially ingest large and dilute fluid loads as food, and they produce copious dilute urine in the field. We examined in the laboratory the renal mechanisms by which such fluid loads are processed. Wattlebirds received one of three liquid diets [a mix of honey, water, and Complan (Boots) complete dietary supplement] of varying concentration (250, 1000, and 1750 mmol/kg, Na+/K+ concentrations of 4/4, 12/15, and 23/30 mmol/l, respectively). We measured renal function via infusion of a filtration marker (14C-polyethylene glycol) from osmotic minipumps implanted intraperitoneally. Wattlebirds consumed volumes of the three diets sufficient to provide nearly equal caloric intakes (approximately 200 kJ/day), and as a consequence had water turnover rates varying from 30 to 200 ml/day (approximately 50–335% of total body water per day). Renal function in the morning, before feeding, did not differ among diet groups (glomerular filtration rate =18 ml/h, urine flow rate =0.4 ml/h). In the afternoon, after feeding, urine flow did vary, from 3 ml/h in birds on the most concentrated diet to 6 ml/h on the most dilute. This was accomplished by varying the rate of tubular reabsorption of water (from a high of >90% on the most concentrated diet to a low of just over 70% on the most dilute), with little variation in the rate of glomerular filtration (mean ∼23 ml/h). Comparisons between dietary intakes and urinary outputs of water and electrolytes suggest that not all dietary water was absorbed from the gut, but that there was significant post-renal reabsorption of Na+. The reduced fractional water reabsorption on the dilute diet was accompanied by a decrease in the circulating concentration of arginine vasotocin (from >4 pg/ml in birds on the two more concentrated diets to <1 pg/ml on the most dilute diet). In contrast, concentrations of aldosterone (10–20 pg/ml) did not differ among diets. Perhaps in consequence, renal fractional absorption of Na+ also did not differ, and so birds on the dilute diet, with their higher urine flows, had higher rates of Na+ excretion and suffered a decreased concentration of Na+ in the plasma.

Spectrofluorometric quantification of neutral and polar lipids suggests a food‐related recruitment bottleneck for juveniles of a deposit‐feeding polychaete population

A growing body of evidence suggests that juveniles of species that deposit feed as adults are more susceptible to food limitation than are conspecific adults. To quantify ontogenetic variations in the nutritional condition of the depositfeeding polychaete Pseudopolydora kempi japonica, I modified existing spectrofluorometric assays of neutral and polar lipids. The hydrophobic fluorochrome Nile red fluoresces yellow‐orange when bound to neutral lipids and red‐orange when bound to polar lipids. The ratio of neutral lipids (energy storage) to polar lipids (cell membranes) provides an index of nutritional condition that is scaled to body size. For individual P. kempi japonica ranging in length from 2 to 12 mm, I quantified the florescence from each lipid class and analyzed sizedependent variations in the neutral/polar lipid ratio. P. kempi japonica showed a size‐dependent increase in the neutral/polar lipid ratio up to a body length of −6–8 mm; little size‐dependent change in the ratio occurred beyond this size. Ontogenetic changes in both particle‐size selection and the assimilated diet of P. kempi japonica display size‐dependent patterns that are similar to the lipid data. Together, the three lines of evidence suggest that P. kempi japonica juveniles experience a food‐related recruitment bottleneck until they grow to −6–8 mm. Once juveniles grow beyond this size, they appear to forage like adults and achieve adult levels of neutral lipid. Because deposit‐feeding benthos ingest a low‐quality and nutritionally dilute diet that will be difficult for small juveniles to digest, ontogenetic niche shifts and food‐related recruitment bottlenecks during the juvenile stage may be common in the population ecology of species that deposit feed as adults.

Nutritional homeostasis in locusts: is there a mechanism for increased energy expenditure during carbohydrate overfeeding?

Maintenance of carbohydrate balance via changes in CO2 output volume was investigated in locusts using a flow-through respirometer. The effect of an imbalance in the dietary protein to digestible carbohydrate ratio on expired CO2 levels was measured in locusts fed one of two synthetic diets [7% protein, 21% digestible carbohydrate (7:21) and 21% protein, 7% digestible carbohydrate (21:7)]. Additionally, the effect of dietary dilution was investigated by feeding locusts one of two diets with a close-to-optimal ratio of protein to carbohydrate, one containing 7% protein and 7% digestible carbohydrate (7:7) and the other containing 21% protein and 21% digestible carbohydrate (21:21). For insects fed unbalanced diets, a higher CO2 output volume was measured during feeding on diet 7:21 when compared with insects fed on diet 21:7. Locusts also expired a greater volume of CO2 during the entire 2h observation period. This response is consistent with specific metabolic control of carbohydrate balance via enhanced respiration. For insects fed balanced diets, the total volume of CO2 expired over the duration of a meal was greater for insects fed diet 7:7 than for those fed diet 21:21, although this was due entirely to meals lasting longer on the more dilute diet. However, the basal level of respiration rate was greater for insects fed diet 21:21 and, as a result, over the entire 2h period, CO2 output volume did not differ between locusts fed diet 7:7 or 21:21. A possible mechanism for enhanced CO2 output volume on the nutritionally unbalanced diet was investigated, namely triglyceride/fatty-acid substrate cycling. There was no evidence for the presence of the thermogenic effect of this particular cycle on locusts as a means for dealing with excess ingested carbohydrate.

Effects of Food Quality and Energy Needs: Changes in Gut Morphology and Capacity of Microtus ochrogaster

Prairie voles (Microtus ochrogaster) were held at 5°C or 23°C and fed an energy concentrate or energy dilute diet in a factorial design. With greater energy needs (temperature effects), small intestine tissue mass, mass with contents, and small intestine length increased by an average of 21%. Caecal length, wet tissue mass, and dry tissue mass increased 12%, 17%, and 12%, respectively, while mass of caecal tissues with contents increased 38%. Reduced energy availability (increased food fiber) accounted for a decrease of 14% in small intestine wet tissue mass, but increases of 11%, 46%, 13%, and 13% in caecal length, mass with contents, wet and dry tissue mass. Large intestine dry tissue mass increased with reduced energy availability, and there was a significant interaction between food and energy effects on wet tissue mass. Dry matter content of prairie vole digesta is high compared to larger herbivores, possibly compensating for a low ratio of gut capacity to metabolic requirement. Changes in organ size are explained in terms of function.

TRANSIENT STEATORRHEA AFTER MILD DIARRHEA OF INFANCY

Chronic and recurrent diarrhea is a recognized antecedent of malabsorption and malnutrition. The relationship of transient mild diarrhea to subsequent malabsorption is unknown. Six normal term infants, for whom 6 d balance control data were available, developed diarrhea in hospital while consuming formula diets (116±22 KcalAg/d). Mean age of onset was 29 d (range 13-37). Treatment: dilute diet (2), Lytren (2), IV + Lytren (2). Full diet was tolerated and all infants clinically well in 3-9 d. Six-day restudy was carried out 7-13 d later while gaining weight on 145±13 KcalAg/d. Results (mean±S.D.) :Apparent N absorption and retention slightly lower and rate of wt gain slightly higher post-diarrhea, neither significantly so. Fecal fat in 9 similarly fed 33 d old infants without diarrhea: 3.3±1.1 g/d, 10.5±3.8% intake (P<0.001). Steatorrhea had resolved 4 wks later in the 2 infants restudied. Mild diarrhea may cause steatorrhea which persists several weeks after illness has clinically resolved. This could be the first step towards malnutrition-chronic diarrhea cycle in marginally fed infants.

Malnutrition studies in Macaca mulatta. V. Effect on biochemical and cytochemical composition of major organs

The effects of control, dilute, and low-protein duets on organ development were evaluated in infant rhesus monkeys. Both experimental duets resulted in growth failure of the cerebral hemisphere, lung, liver, kidney, and muscle and, with few exceptions, in their total organ contents of water, protein, lipid, glycogen, DNA, and RNA. Calculation of the various ratios for biochemical indices per mg of DNA indicates that with the exception of increased glycogen:DNA ratios in lung of animals fed the dilute diet, increased lipid:DNA ratios in liver, and reduced glycogen:DNA ratios in muscle of animals fed the low-protein diet, all other biochemical profiles of the cellular populations of organs were comparable to control values. Accordingly, the small organ size and reduced organ content of the various biochemical indices of growth appear primarily due to the reduced cellular populations of these organs. The reduced cellular populations reflect failure of the normal miotic processes of infancy to occur, with or without loss of cells already present at the onset of the malnutrition phase. If no cell loss is involved, it is speculated that normal indices of organ growth may still be possible through the processes of "catch up" growth which accompany nutritional rehabilitation.

Influence of caloric density on energy intake by dairy cows.

Twenty-four Holstein cows were fed mixed diets of alfalfa hay and concentrate in a series of periods to determine the relationship between caloric density (mcal digestible energy/liter) of the diet and energy intake. Five diets with caloric densities of .58, .63, .68, .84, and 1.17 (as-fed form) were used. Steers were fed the diets in digestion trials to determine maintenance digestibility. Intake of digestible energy was adjusted for intake. Means of digestible energy intakes (kcal/day per kg. 75) were: 291.7, 324.0, 370.0, 371.4, and 369.1 for diets with caloric densities of .58, .63, .68, .68, .84, and 1.17. Physical fill was limiting for the two most dilute diets. The diet with caloric density of .68 represented the point above which physiological regulation was employed by the animals. The relationship between digestible energy intake (kcal/day per kg-75) body weight (Y) and caloric density (mcal/liter dry matter, as fed form) (X) was Y = 759.2X-148.4, simple correlation .99, for diets with caloric densities of .58, .63, and .68. Potential uses of this relationship in maximizing forage utilization and formulating diets to meet specific energy requirements are cited.

Malnutrition studies in Macaca mulatta. IV. Energy and protein consumption during growth failure and “catch-up” growth

Infant rhesus monkeys were fed either a control, dilute or low protein diet from 1 to 7 months of age, and the control diet from age 7 to 12 months. All diets were fed ad libitum. Curves were fitted for energy and protein consumption and for growth in weight, length and head circumference. Both experimental groups developed increasing deficits of energy and protein consumption during the undernutrition experiment. With nutritional rehabilitation, the animals previously fed the dilute diet immediately increased their consumption of energy and protein to levels appropriate for age. Those previously fed the low protein diet showed an increased nutrient uptake, but one more appropriate for size peers. Reduced growth velocity occurred with both experimental diets. "Catch-up" growth, and growth velocity per unit diet energy and protein was most obvious for body weight, but recovery from growth deficits was most complete for growth in head circumference. Nutrient deficits accumulated by animals fed the dilute diet were not recovered during catch-up growth; catch-up growth occurred in animals previously fed the low protein diet even though cumulative nutrient deficits were increasing.

Effect of ADH on Rat Renal Papilla, an Ultrastructural and Cytochemical Study

Diabetes insipidus and compulsive water drinking are representative of two categories of antidiuretic hormone (ADH) lack. We studied a strain of rats with congenital diabetes insipidus homozygote (DI) and normal rats on an isocaloric fortified dilute milk diet. In both cases, the collecting tubules could not concentrate urine. Special staining techniques, Alcian Blue-PAS for light microscopy and lanthanum nitrate for electron microscopy were used to demonstrate the changes in interstitial mucopolysaccharides (MPS). The lanthanum staining was done according to the method of Khan and Overton.Electron microscopy shows cytoplasmic lesions, vacules, swelling and degenerating mitochondria and intercellular spaces (IS) in the collecting tubule cells in DI and rats on milk diet.

Palatability and caloric density as determinants of food intake in hyperphagic and normal rats

Female albino rats with lesions of the ventromedial hypothalamus and without any lesions were presented with powdered diets, the caloric density and palatability of which were varied independently by adding kaolin and sodium saccharin or confectioner's sugar. As the dilution of the unsweetened diet increased above 20% the lesioned rats decreased food consumption more than did the controls, and they increased consumption less than did the controls over successive days of exposure to the diluted diets. Sweetening the dilute diets usually produced a larger increase in food consumption among the hyperphagic rats, especially those in the dynamic phase, than among their controls. The data are interpreted in terms of the hypothesis that lesions of the ventromedial hypothalamus remove or attenuate the long term influence of nutritional balance, leaving body weight to be adjusted to a set point defined by the interaction of prevailing values of other stimuli such as diet palatability that are known to influence initiation and termination of eating.